1. Field of the Invention
The present invention relates to an apparatus and a method for forming a coating layer, particularly to a die set and a method for forming a coating layer of multiple stripes composed of two materials A and B adjacent to each other in a repeated ABAB pattern.
2. Description of Related Art
U.S. Pat. No. 4,106,437 discloses an apparatus for multiple stripe coating of a web with liquid coating composition which is comprised of a hopper having a pair of spaced lips and a pair of shims mounted in face-to-face arrangement within the hopper and positioned between the spaced lips. One of the shims is provided with a plurality of open-ended channels while the second shim is equipped with a plurality of projecting portions, corresponding in width and location to the desired stripes, which are in alignment with the open-ended channels and project beyond the open ends thereof. The apparatus is capable of carrying out multiple stripe coating of a web at high speeds and with a high degree of precision in regard to stripe width and registration.
U.S. Pat. No. 4,324,816 discloses extrudable materials which exhibit a decrease in viscosity as the shear rate is increased, such as magnetic dispersion striping materials, and are suitable for extrusion coating in the form of a narrow stripe. The stripe has predetermined uniform cross-sectional dimensions including substantially uniform thickness, and is coated onto a moving web by means of a die maintained in a predetermined spaced relation with the web. The die has two or more bores through which the extrudable material is extruded in columns onto the moving web to form the stripe thereon.
Japanese patent publication No. 7-136568 A discloses a method for simultaneously forming continuous coating surfaces of the same thickness free from joints in the transverse direction of a band-shaped material by segmenting a coating liquid passage consisting of manifold parts and a slit part in a transverse direction and supplying different kinds of coating liquids in the respective segmented passages.
Japanese patent publication No. 7-195015 A discloses methods for producing multiple stripe coating product. To easily control the coating width of a coating solution and to make accurate stripe coating possible, a liquid-permeable sheet is placed in a slot of a coating die to discharge a coating solution.
Japanese patent publication No. 8-038972 A discloses methods for producing multiple stripe coating product, in which continuously coating a stripe pattern consisting of plural colors on a belt-like material with one coating process and also easily changing the width of a stripe are made possible. A manifold is provided in the inside of a metallic material apart from a slot part for discharging a coating material. A plurality of through-holes communicated with the slot part, and a plurality of coating liquid feed-ports communicated with a coating liquid feed device at the outside of a die main body are formed on the manifold.
Japanese patent publication No. 8-099056 A discloses methods for forming a coating film in a stripe pattern with no fluctuation width and thickness by projecting a front block more than a back block toward a base material and forming jetting-out holes for a coating material in the flat face of the back block. In this prior art, a nozzle is composed of a front block positioned in the upper stream side in a base material running direction and a back block positioned in the down stream side. The front block of the nozzle is projected toward the base material side as compared with the back block. When a base material is moved along the surface of the nozzle composed in this way, the base material moves along the curved face of the front block and continuously moves above the back block of the nozzle in which jetting-out holes for a coating material are formed. Consequently, a coating film in a stripe pattern with no fluctuation of width is formed on the surface of the base material by coating.
When a coating product of multiple stripes is made, interfaces of different coating solutions will be affected by coating thickness thereof and physical properties of coating solutions, such as the viscosity and the surface tension. These will result in a tendency that the borders of the coating solutions extend outward and become thin, and thus a coating layer of inferior uniformity and low interfacial quality is formed. The problems become worse, if the multiple stripe coating layer is laid as an intermediate layer of multiple layer coating product. Therefore, a technique of precise multiple stripe coating in ABAB pattern becomes essentially important, due to a necessity of extreme uniformity and an approximately rectangular cross section for the multiple stripe coating layer.
In the aforesaid prior art methods for forming a coating in an ABAB pattern, it is difficult to ensure a definite and precise interface between two adjacent coating solutions A, B and even harder to generate an intermediate layer of multiple stripe in a multiple coating layer structure. Among them Japanese patent publication Nos. 7-136568, 8-038972 and 8-099056 have great disadvantages in non-uniform width of stripes and ambiguous interfaces of coating solutions A, B, because the two coating solutions are contacted with each other outside the die set.